The X-ray transient MAXI J1820+070 was discovered on 2018 March 11.5347 UT by MAXI (Monitor of All-sky X-ray Image; ATel #11399). It was matched with the optical counterpart ASASSN-18ey (ATel #11400), which was discovered by the ASAS-SN project on 2018 Mar. 06.59 UT (list of ASAS-SN Transients).

In support of multiwavelength observing campaigns underway, being planned, and in development, AAVSO observers are requested to monitor this active black hole X-ray binary.

Dr. Gandhi writes: "At present, we find that the source shows red flaring on timescales apparently down to milli-seconds. So my primary recommendation would be to use redder filters and as short exposures as possible. The source appears to be approaching V404 Cyg levels of brightness, so that could be a useful comparison. It is not obvious that it displays the spectacular variations that V404 Cyg showed on ~minutes to hours and days. But there is clear and strong variability on timescales of ~seconds and less.

"Latest observations now find [g'~12.03 mag and i'~12.24 (ATel #11439)], so the outburst continues to brighten (quickly) for now, and we may expect a transition in the source properties soon, assuming this is a canonical black hole binary. Observations over the next ~weeks (or until the source fades, if that happens earlier) would be very useful to catch the long-term evolution. Unfiltered [photometry] is acceptable as long as there is a consistent dataset."